This invention relates to biaxially oriented nonwoven fabrics and more particularly to nonwoven fabrics having low fiber density and high fiber density areas and their uses as adhesive tape substrates and the like, wherein said high fiber density areas have low fiber density strands of fibers entering therein from at least eight different directions, each of said strands having substantially parallelized fibers therein.
In U.S. Pat. No. 3,969,561, of common assignee, a biaxially oriented nonwoven fabric was described; however, this was essentially a striped fabric of alternating high and low fiber density stripes, the fibers of the alternating stripes being oriented substantially normal to the other. While this fabric has an improved tensile strength, its tear strengths in the machine direction and cross direction are not equal or even nearly so. If one were to attempt to tear straight across the fabrics, it would be nearly impossible to achieve.
A prior art product that has a somewhat similar appearance to this invention is described in a number of patents of which U.S. Pat. No. 2,862,251 is typical, particularly with reference to FIGS. 49-58. This patent teaches how to make a tufted apertured three-dimensional fabric having budded protuberances, consolidated "flat pack ribbons" extending in the direction of the general orientation of the web fibers, and smaller consolidated "flat bundles" which extend between immediately neighboring buds in a direction generally transverse to the direction of main fiber orientation. By starting with an isotropic web, an element of parallelism is introduced in as many as six (6) directions emanating from the tufted three-dimensional bud portions. Using this method, a uniform web is first formed, treated and then rearranged by hydraulic forces. However, it should be apparent to those looking at the products described therein that all of the products produced thereby result in an apertured and tufted fabric. The apertures or holes in the fabric reduce the fabrics usefulness for many purposes, while the tufts restrict the uniform tearability of the fabric.
Accordingly, it is an object of this invention to produce a fabric having easy tear characteristics in both the cross and machine directions of the fabric so as to facilitate the use of this fabric as a substrate for medical and industrial adhesive tapes, other tape products and other materials and products where such characteristics are important.
Another object of this invention is to provide an aesthetically pleasing, light-weight, octa-directionally oriented and highly drapeable fabric.
A further object of the instant invention is to produce a fabric having all of the above desirable characteristics in a light-weight nonwoven fabric that is rather "uniformly covered" and is substantially free of apertures.
Still another object is to produce a fabric that can be used as a spacer in a composite structure wherein approximately 162/3% to 25% of the area of the space fabric acts as the thick spacing material.